"Sigourney and I have a long creative history, dating back to 1985 when we made 'Aliens,'" Cameron said, according to Deadline. "We're good friends who've always worked well together, so it just feels right that she's coming back for the Avatar sequels. Her character of Grace Augustine, as fans know, died in the first movie, so she's playing a different and in many ways more challenging character in the upcoming films. We're both looking forward to this new creative challenge, the latest chapter in our long and continuing collaboration."

The currently-untitled "Avatar" sequels will be filmed back-to-back, with production starting later this year. The first follow-up film will be released in December 2016, with the second following in 2017 and the third a year later.

The original "Avatar" was released in December 2009 and went on to become the top-grossing film of all time, earning $2.8 billion at the worldwide box office.